Elastomeric forming die

ABSTRACT

A solid die pad of elastomeric die material and a holder for the die pad having converging sides; the die pad being conformingly shaped to fit between and be supported on said converging sides.

O United States Patent 1 [111 3,760,622 Mansell Sept. 25, 1973 [54] ELASTOMERIC FORMING DIE 2,783,727 3/1957 Hofi'mann 72/57 2 2 9 l2 9 [76] Inventor: Manse, 242 Chartwe 3:228:38 7x922 Sr. Oakville, Ontario, Canada [22] Filed: 1972 Primary Examiner-Lowell A. Larson [21] App]. No.5 222,537 Attorney-Rogers, Bereskin & Parr [52] US. Cl 72/57, 72/465, 72/DIG. 14 51 rm. Cl 821d 5/00 [57] ABSTRACT [58] Field of Search 72/57, 465, 466, A Solid die pad ofelastomeric die material and a holder 72/DIG' 14 for the die pad having converging sides; the die pad References' Cited being conformingly shaped to fit between and be sup- UNITED STATES PATENTS 10/1966 Achler et a1. 72/465 ported on said converging sides.

1 Claim, 4 Drawing Figures templated by the invention.

ELASTOMERIC FORMING DIE The invention relates to a method of press forming formable material, e.g. plates, sheets, bars and so forth, as well asto tooling for carrying out the method of the invention, namely, a die assembly installable in a forming machine for co-operation with a male die in the forming of the materials aforesaid.

For the sake of simplicity and unless dictated otherwise by the context hereof, all subsequent reference to sheet material and sheet metal is meant to comprehend and include as well plate and bar materials and metals.

Similarly, the forming machinery contemplated by the invention may henceforth be compendiously designated as presses to indicate thereby that the material operated upon is pressed into the required shape.

In the forming of the formable sheet material, e.g. plate, sheet or bar material as aforesaid it is known to use a female reaction element which is formed in whole or in part of an elastomer such as urethane having appropriate hardness and other qualities which adapt it for this service; such elastomers, hereinafter referred to as elastomeric die materials, being also con- One essential characteristic of dies formed of such substances is that when impressed by a male die under appropriate circumstances, they will deform temporarily to a conforming female configuration; the die substance being displaced against the holder or retainer in which it is confined.

One example of a die assembly. as herein visualized may be found in Achler et al. US. Pat. No. 3276,239

which is directed principally to a retainer for an elastomeric die pad. The die assembly disclosed in this patent is generally typical of the known prior art; the retainer having parallel sidewalls which are both generally perpendicular to its bottom or bed and providing accommodation for an elastomeric die pad of conforming cross-section.

At this point, it appears advisable to observe that in the prior die assembly described, the bottom of the retainer served as the reaction base for the. pad. That is to say, the pad. being essentially supported thereon, the said bottom received and consequently bore the brunt of the forming pressure exerted on the pad by the male die and hence, in turn, provided the main reactive base for the pad. For this reason, it is believed, this type of die assembly appeared to require the employment of heavy pressures in order to effect the desired material forming.

Conversely, the invention is predicated on a new concept of die construction which precludes the necessity for heavy pressures while conducing at the same time to better forming with less wear on the die pad in particular, by minimizing the extent to which the male die is required to penetrate the pad in order to shape the interposed material; this being a principal object which the invention seeks to achieve.

This object and others, in part hereinafter stated and in part clearly obvious from the contents hereof, are achieved by the provision of a die assembly comprised of a pad of elastomeric die material in a retainer having sidewalls which provide lateral confinement-for the pad; one at least of said sidewalls providing also a reaction base for the pad; the pad sides conforming substantially to the two retainer sidewalls.

The invention is exemplified by the preferred embodiment thereof which is illustrated in the appended drawing and hereinafter described by way of example only; like parts of the invention throughout the several views of the drawing being identified by like reference devices.

In the Drawing,

FIG. 1 is an isometric view of the fragment of a die according to the invention with a piece of sheet material sandwiched between it and a male die;

FIG. 1 is an elevational view of the structure of FIG. 1 with dotted lines indicating the characteristic behaviour of the present die;

FIG 3. is an elevational view on a reduced scale corresponding somewhat to FIG. 1 but showing the probable distribution of pressure and reaction forces therein, and

FIG. 4 is an elevational view corresponding to FIG. 3 showing the relative status of the parts upon completion of the forming operation.

As is shown by the drawing, the illustrated die assembly A being'thespecific embodiment of. the invention selected for the exemplary purposes of this submission, comprises the'holder or retainer 2 for pad 4 illustrated in the drawing. For reasons which will appear, it will be understood that pad 4 has a snug fit in retainer 2 as illustrated. 7

As will be observed, the retainer 2 has sidewalls 6-6 which in the present embodiment, coverge towards bottom of the retainer 2. Said bottom may be formed and constituted by and at the juncture of said retainer sidewalls 6-6 as in FIG. 1. In addition, it will be observedfurther that the pad sides 7-7 conform substantially to the retainer walls 6-6 upon which,.as is obvious, the snugly fitting pad 4 is actually supported and from which it derives its main reactive potential. Thus, each sidewall 6 of the present retainer 2 will be seen to constitute a reaction base for the present pad as well as co-operating with the other sidewall to form a pad trough or recess 8. 1

In point of fact, many circumstances can be visualized in which the pad 4 can expediently be given the trapezoidal shape which would result if pad 4 were truncated along dotted line x shown in FIG. 1;.said

trapezoidal shape precluding pad 4 from actually reaching recess bottom 10, not only without impairing but, perhaps even enhancing the pad function. Besides being angular as in FIG. 1, said retainer bottom 10 may also be constituted by the level floor in FIG. 3.

FIGS. 2 and 3 seek to illustrate in graphic or schematic form the advantages of the die assembly A herein visualized. However, it should be emphasized that pressure reactions purporting to be indicated by arrows y in FIG. 3 are assumed and hypothetical only.

Briefly stated, it will be apparent that a substantial component of the pressure exerted by male die 12 against the pad surface 13 is transmitted to and reaches each inclined retainer sidewall 6 which, of course, serves also as a reaction base for the pad 4 as previously described, and as suggested by FIG. 3. In practice, it has been noted that the reaction of pad 4 to male die pressure has been, accordingly, to induce bulging or selling of the pad material in the only direction in which it can conveniently go namely, upwardly towards male die 12 as generally shown in FIG. 2, 3 and 4. In

" turn, this results in the deformation and massing of the pad surface 13 about the terminal 14 of the male die 12 thereby inducing the work 16 the interposed sheet material to wrap itself about said terminal 14.

Moreover, apparently because of its confinement between the convergent retainer sidewalls 6-6, it has been found that the rate at which the pad 4 bulges as aforesaid increases as the die terminal penetrates further into the pad material thereby intensifying the wrapping effort of work 16 about said die terminal 14. This reaction is shown in FIG. 2 which illustrates, in dotted lines, two penetrations of male die 12 into pad 4 and the resulting bulging of the latter.

In this way, the forming of the work 16 about die terminal 14 is capable of being achieved with comparatively' minimal penetration of the latter into pad 4.

Besides the foregoing, other advantages also appear to flow both directly and indirectly from the herein visualized structure of retainer 2 and pad 4. For example, the die assembly A is believed to provide and have a forming capability as well as the achievement of superior forming under low force applications. Another advantage which seems to flow from the design of the present die assembly A is the reduction of marking or scratching of the work during the forming operation as well as reduction of wear on the impression surface of the pad.

Thus with very limited penetration, die terminal 14, the co-operating pad 4 and retainer 2 co-act to produce reactive deformation forces operating on the work 16 to procure initial wrapping thereof about the flanks of the die terminal 14 and subsequent further penetration, as indicated in FIG. 2, produces sufficent pad reactive forces, owing to the non-linear moment of deformation, to complete the forming of the work without total or even major penetration of the die 12 into the pad 4.

In attempting to explain the energy relationships involved, initial penetration as in FIGS. 2 and 3 is believed to produce elastic compression of pad 4, together with a transverse Poisson expansion laterally. Owing to the inclination of the abutting retainer sidewalls 6--6, the Poisson expansion probably produces an upward force acting upon the pad, tending to move the pad extremities towards the male die 12. However, the reduced thickness of the pad extremities leads to a diminishing section inertia or stifiness, so that further penetration of the pad 4 produces progressive upward deformation thereof into corresponding material deforming relation with the work 16 and die 12. It is further hypothesized that suitable selection of section form and proportion permits a wide range of use in which the pad 4 operates predominantly within its elastic limits.

In the preferred form of the invention selected for the exemplary purposes of this submission, the pad sides 7-7 converge from pad surface 13 to pad bottom 18 to impart to the pad 4 a width which diminishes progressively from pad surface 13 towards its bottom 18. Moreover, as has been said, the pad 4 may have the triangular profile section shown in full lines in FIG. 1 or the trapezoidal conformation of FIGS. 3 and 4 created by truncating it along the dotted line x in the same view. In addition, the pad dimensions may be such as to elevate its surface 13 somewhat above the top of the retainer 2.

It must be understood, however, that this particular shaping of the parts does not necessarily represent a contant; there being many circumstances in which the pad proportions and profile may require some deviation from the present form in order to suit specific purposes. Generally, however, the form of the pad 4 herein selected to demonstrate the inventive idea is sufficient .for the purpose to the extent that it illustrates the concept of inclining at least one retainer sidewall 6 to the thrust axis of the male die 12 whereby, with a properly fitted, shaped and confined pad 4, the thrust or pressure of the said male die 12 may well be reflected as in FIG. 3 to wrap the pad material upwardly about the terminal 14 of the male die 12.

What I claim is:

1. A die pad assembly co-operable with a male die for press forming sheet material therebetween, the die pad assembly comprising:

a pad holder having a longitudinally extending recess, the recess including a pair of mutually inclined side walls disposed symmetrically about a longitudinally extending plane containing the path of travel of the male die;

a pad of an elastomeric material, the pad having a pair of sides disposed angularly one with the other, the angle between these sides being substantially equal to the angle between said side walls, whereby the pad is seated in the pad holder with respective said sides in contact with corresponding said side walls, the pad also including a top surface disposed generally perpendicularly to said plane and being symmetrical about the plane; and

the proportions of a transverse cross-section of the pad being such that upon placing said sheet material on the top surface of the pad and engaging the male die, the pad is compressed between leading extremities of the male die and the side walls to cause the sheet material to bend about the male die.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,760 ,622 Dated September 25, 1973 Inventofl Ivor ll It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Convention Priorityis claimed on the basis of Great Britain Appllcatlon serial No. SN 6865/71 filed-on Marchfl5, 1971,

Signed and sealed this 17th day of September 1974.

(SEAL) Y Attest: 3 I McCOY M. GIBSON JR; 7 r C. MARSHALL DANNY [Attesting Officer 7 Commissioner of Patents FORM PO-1050 (10-69) UjSCOMM-DC scene-P09 Aims. GOVERNMENT Pnm us omcr: I!" case-s34, 

1. A die pad assembly co-operable with a male die for press forming sheet material therebetween, the die pad assembly comprising: a pad holder having a longitudinally extending recess, the recess including a pair of mutually inclined side walls disposed symmetrically about a longitudinally extending plane containing the path of travel of the male die; a pad of an elastomeric material, the pad having a pair of sides disposed angularly one with the other, the angle between these sides being substantially equal tO the angle between said side walls, whereby the pad is seated in the pad holder with respective said sides in contact with corresponding said side walls, the pad also including a top surface disposed generally perpendicularly to said plane and being symmetrical about the plane; and the proportions of a transverse cross-section of the pad being such that upon placing said sheet material on the top surface of the pad and engaging the male die, the pad is compressed between leading extremities of the male die and the side walls to cause the sheet material to bend about the male die. 